The present invention relates to an energy absorbing structure for a vehicle body side portion using an air bag.
In recent years, an attempt is made in some vehicles to arrange an air bag for absorbing and relaxing an impact force in a front portion of a passenger room in view of protection of passengers upon collision. In practice, remarkable effects have been experienced.
Passenger protection upon collision of vehicles must be considered not only for a head-on collision but also for a side collision of vehicles. From this point of view, for example, Japanese Utility Model Laid-Open No. 1-117957 proposes a mechanism wherein an air bag is arranged in an armrest of a door constituting a vehicle side portion, and is unfolded toward the interior of a passenger room upon side collision of vehicles, thereby absorbing and relaxing an impact force acting on a passenger.
In general, an air bag is unfolded (inflated) by a gas injected at high speed from an inflator into the air bag, and when a gas is filled in the air bag in a sealed state, a repulsion force of the air bag becomes too strong, and passenger protection performance may be impaired accordingly. For these reasons, a vent hole for appropriately exhausting a gas is formed, and when the passenger abuts against the unfolded air bag, the air bag is collapsed while exhausting the gas from the vent hole, thereby assuring an unfolded state suitable for absorbing a shock.
However, such a structure has an inevitable drawback in that a gas amount becomes short after an elapse of a predetermined period of time from the beginning of unfolding, and the air bag becomes deflated so as not to assure a sufficient shock absorbing effect since the gas amount injected from the inflator is not infinite but is limited.
Meanwhile, a time from when a side collision of vehicles occurs until a passenger actually collides against an inner wall portion in a passenger room is not constant. For example, assume the following side-collision state. That is, in a state wherein a passenger sits on a driver's seat of a vehicle in which air bags are arranged in both right and left door portions, if another vehicle collides against the door portion on the driver's seat side, the passenger temporarily moves toward the door on the driver's seat side by the inertia immediately after the collision (FIG. 5), and then moves toward a front passenger's seat by a counterforce (FIG. 6). For this reason, there is a large time lag between a timing at which the passenger collides against the door on the driver's seat side and a timing at which he or she collides against the door on the front passenger's seat side.
Therefore, the right and left air bags wait for the passenger in the optimal unfolded state under such a condition. However, by the time the passenger is thrown out toward the front passenger's seat side, the air bag on the front passenger's seat side may have begun to be deflated from the optimal unfolded state.
The conventional mechanism does not sufficiently consider a variation in collision timing of a passenger against the inner wall portion of the vehicle body, and there is a room for improvement in terms of improvement of passenger protection performance.